1. Field of the Invention
The present invention relates to internal combustion engines, and in particular to the pistons associated therewith wherein the piston body is fabricated from one material, preferably a metal, and the piston head is fabricated of ceramic or ceramic composite material and joined with the metal piston body.
2. Description of the Prior Art
Pistons are an integral part of most all internal combustion engines for the transfer of the power contained in the fuel/air mixture combustion to a crank shaft, which in turn through various gearing mechanisms transfers that power to the wheels of a land vehicle, the propeller of a water vehicle, or the propeller of an airplane. The piston is tightly fitted within the cylinder of an internal combustion engine and reciprocates upwardly and downwardly within the cylinder in response to the combustion of the fuel/air mixture, and the rotation of the crank shaft to which it is secured by means of a connecting rod.
The piston itself is normally fabricated of two primary elements. First there is the piston body, which is cylindrical in shape having a plurality of annular grooves for the receipt of piston rings to effectuate a seal with the wall of the cylinder within which it reciprocates. The piston body has means positioned on its underside for the secure connection of one end of a connecting rod, the opposing end being connected to a crank shaft. The upper portion of the piston body is normally fitted with a separately fabricated piston head which would normally be welded to the piston body about their common circumferential peripheries. It is the piston head which is exposed to the heat of combustion in the cylinder. It is also the piston head which has been the subject of much redesign in order to improve the combustion within the cylinder by inducing turbulence to create a more homogeneous combustion. Piston heads have evolved from a planar circular head, to heads having an upper surface resembling a single wedge shape or multiple wedge shapes to piston heads having a dome shape which are commonly referred to as hemi-heads.
Internal combustion engines which incorporate piston bodies and piston heads made of the same or similar metal material performed adequately with conventional fuels, such as gasoline and diesel. Engineers and designers would always look for improvements to the piston body and piston head arrangement in order to improve efficiency and performance. One drawback to the conventional piston body and piston head arrangement is that with both of the elements being fabricated from the same material, the heat of combustion within the cylinder will elevate the temperature of the piston head and the piston body due to their similar characteristics. This is not critical with respect to conventional internal combustion engines operating on conventional fuel, such as gasoline or diesel, since this heat transfer will not have deleterious affect until many hundreds of thousands of miles are put on the engine.
However, with the advent of use of alternative fuels such as ethanol, or natural gas, or hydrogen, there is a need because of the heat of combustion to seek alternative materials application to the fabrication of a piston head. An ideal material for the piston head would be that of a ceramic or ceramic composite, which performs superior to metal at high temperatures without deterioration or degradation.
Attempts have been made in the past to mate a ceramic piston head to a metal piston body, but those attempts have heretofore failed to provide for a metal piston body and ceramic piston head structure of sufficient durability normally resulting in separation of the body and head.